Truffles (Genus: Tuber; Family: Tuberacea; Order: Pezizales) are ascomycetes fungi which live in symbiosis (ectomycorrhizae) with oaks, beech, hazels, etc. Among the 60 species that exist, only a limited number of species are praised for their aroma and for their taste, including the black Périgord truffle (Tuber melanosporum), the White Piedmont truffle (Tuber magnatum); the summer truffle (Tuber asetivum), another black truffle (Tuber brumale) and the “small white Italian truffle” (Tuber borchii). The world production is in constant decline: about 1000 tons of truffles were produced at the beginning of the 19th century, but only 80 to 150 tons are produced nowadays.
For more than 50 years, humans have been planting trees which roots had been inoculated with truffles. Less than 5% of these trees produce truffles and this usually only after 5-10 years due to the poor understanding that human have of truffle biology.
Truffle aroma is made up of about 50 volatiles, which are hydrocarbons containing alcohol, ketone, aldehyde and ester functional groups and also sulfur atoms. Different truffle species have a distinct aroma from each other because they produce species specific volatile compounds. Some volatiles are also common to all truffle species; however they are produced by each species in specific quantities. Taken separately none of these volatile compounds smells like truffle fruiting bodies, however once the right compounds are mixed in the right proportions, the mixture reproduces the aroma of truffle fruiting bodies.
Nowadays truffle aromas can be obtained using truffle fruiting bodies and trapping their aroma into a solid substrate (i.e. rice, some cheeses or liver such as the French “foie gras”) or a liquid substrate (oils, creams) by extraction or maceration. Another way to obtain black truffle aroma is to use synthetic truffle aromas basically composed of dimethylsulfide and 2-methylbutanal according to the French Patent FR 86 10871 A1 (Delmas, Institut National Polytechnique de Toulouse) or composed of dimethylsulfide and methylethylketone (also known as 2-butanone) according to the Italian Patent IT 1215936B (SENTOSA S. A. S MILANO).
The use of the synthetic compounds in specific proportions described in the French and Italian patents mentioned in the previous paragraph do not permit, according to the European legislation, to use the label “natural truffle aroma” for products that contain those synthetic mixtures. The invention described herewith specifically permits to obtain such a “natural aroma” of white or black truffle, since the aroma compounds are directly derived from truffle mycelium.
Additionally, since the creation of synthetic truffle aromas, international experts agree that synthetic truffle aromas does not have the complexity and nuances of natural truffle aromas, simply because synthetic aromas only contains a limited number of molecules (2 to 5 in total) compared to natural aromas that contains much more constituents (more than 20 volatiles). Furthermore the production costs of natural truffle aromas keeps on rising due to the decline observed in the worldwide production of truffle fruiting bodies (Fauconnet and Delher 1998; Hall and Yun 2001).
Furthermore the aroma analysis performed so far on the truffle mycelium of Tuber borchii (the “small white Italian truffle”) showed that even though many aroma molecules are spontaneously produced by the mycelium, they do neither reproduce the smell nor the complexity of fresh truffles (Tirillini et al., 2000; Splivallo et al., 2007). Additionally the American company Truffle International which produces truffle mycelium in hydroponic cultures acknowledges that the taste and aroma of their products clearly differs from the one of truffle fruiting bodies, mostly due to a very low concentration of sulfur containing volatiles (Fields, 2007; see also the web site of the company <<Truffles International>> http://www.truffiesinternational.com/truffle_science.html).
It should be stressed that most culture media used so far to grow truffle mycelium contained low concentrations of amino acids (traces), simply because these culture media are themselves derived from plants (i.e. the potato extract “potato dextrose broth” used in Splivallo et al., <<Discrimination of truffle fruiting body versus mycelial aromas by stir bar sorptive extraction>>, Phytochemistry (Amsterdam) October 2007, Vol. 6668, No. 20, pp 2584-2598). Amino acids are as a matter of fact often used in microbiology to favor the growth of microorganisms. In the case of truffle mycelium, a low concentration of amino acids (traces) is however not sufficient to induce the production volatiles characteristic of the aroma of truffle fruiting bodies.
The patent JP 2005295858 also recommends using amino acids to favor nitrogen uptake by black truffle mycelium thus inducing its growth. The authors of the latter patent however admit that truffle mycelium obtained in such a way does not smell like truffle fruiting bodies, and even recommend drying the mycelium to facilitate its handling/marketability of their product (which surely results in the loss of any aroma compound).
In summary, the invention described in the present patent allows to induce the production of volatile compounds in a targeted manner and as a whole obtain a mixture of volatiles which are characteristic of the natural aroma of truffle fruiting bodies (sulfur containing volatiles and other key volatiles of truffle aroma).
Considering that synthetic truffle aroma is poorly accepted by consumers, and considering the very high prices reached by natural truffle aroma obtained from fruiting bodies, the present invention also offers a solution to the market by defining an alternative and cheaper process to obtain natural truffle aromas. The present invention also permits to reduce overharvesting of truffles in the wild, thus decreasing the ecological pressure on the fungus.